1. The main matrix components of bone are calcium salts in the form of hydroxyapatite, which makes bones hard, and collagen, which confers resiliency to the bone. Since the calcium salts are embedded in a collagen matrix, even if a shock is hard enough to break the calcium, the collagen fibers absorb the shock.
2. Vertebrate joints include the immovable joints, such as the sutures in the skull, the slightly moveable joints, such as the joints between the vertebrae in the spine, and the freely moveable joints, such as the hip or shoulder joints.
3. The origin of a muscle is where it attaches to the stable, or nonmoving bone. The insertion is in the bone that does the moving when the muscle contracts. Synergists act together to facilitate a movement, such as one group of muscles stabilizing the shoulder so that the biceps can contract. Antagonistic muscles perform opposite functions; when one is contracted the other is relaxed, such as the biceps and triceps brachii of the arm.
4. A myofibril is a bundle of actin or myosin within the muscle fiber (muscle cell). A sarcomere is a repeating contractile unit in skeletal muscle that is connected end-to-end. They are connected by a disc of protein which forms the Z line. Myofilaments are the individual actin and myosin fibers composing the myofibril.
5. Thick filaments are composed of myosin. Thin filaments are composed of actin.
6. The resting myosin head attaches to the actin filament at the angle between the S-1 and S-2 units, which is 90_. A power stroke reduces the angle between S-1 and S-2, resulting in the advancement of myosin filament relative to the actin filament. The globular head detaches from the actin filament and the head returns to the previous 90_ angle configuration and starts the cycle again. ATP is used at the power stroke step, when the angle between S-1 and S-2 is reduced.
7. Contraction is initiated by a nerve impulse. The chemical released is acetylcholine. It depolarizes the muscle membrane which opens calcium channels in the muscle membrane. When calcium is present in the sarcoplasm, cross-bridges between the actin and myosin can form, and contraction is initiated.
8. The nervous system can control the relative strength of muscle contraction through summation, which is varying the number of times a nerve fires to make a muscle contract; and through recruitment, firing impulses triggering more or fewer motor units.
9. An isometric muscle contraction involves contraction of a muscle without moving a bone or shortening of the muscle. An isotonic contraction moves a bone at a joint and shortens the contracting muscle, which requires more ATP than an isometric contraction.
10. Cardiac muscle is striated, as is skeletal muscle, but the cells are highly branched and contain only one nucleus. Cardiac muscle cells communicate with one another through gap junctions in intercalated discs, ensuring contraction of the myocardium as a unit. Cardiac muscle is self-exciting, although heart rate can be influenced by the nervous system. Impulses travel through the tissue in a wave, providing for coordinated contraction of the heart.
11. In smooth muscle, thick and thin filaments are not organized into sarcomeres. Calcium is required for smooth muscle contraction, but it comes from extracellular fluid rather than from a sarcoplasmic reticulum, which is absent in smooth muscle cells. Smooth muscle has the ability to contract even when it is greatly distended, which would not be possible because of tearing in skeletal muscles.